Conventionally, composting has been conducted to realize effective utilization of waste materials in food industry, food processing industry, livestock industry, and the like where organic waste materials are most likely to be produced In such municipalities that deal with urban garbage, composting has also been conducted for the purpose of volume reduction or conversion to stable substances. In particular, may organic waste materials disposed from food processing factories and the like are likely to have high water content at the time of being disposed from these factories. Therefore, if it is left alone during summer, a variety of bacteria may grow, putrefaction may begin, and unpleasant odors that mainly come from putrefaction odors may occur. Then, there arises a problem in view of the environmental protection.
Further, since the waste materials have in general high moisture content when composted, the anaerobic environment may be partially generated within a fermentation vessel. Then, the fermentation operation may be conducted under the mixture condition of anaerobic bacteria and aerobic bacteria, so that the fermentation efficiency is low. Typically, several months are required until protein, fat, or the like are decomposed and stabilized as compost.
Still further, since the fermentation efficiency is low as described above, unpleasant odors caused by amines, ammonium, or the like as major component are always carried while compost is produced. In addition, the sufficient fermentation operation may not be possibly conducted, the obtained product may be fermented again when it is used as compost, and then unpleasant odors may possibly occur. Furthermore, it cannot be avoided to accumulate, during composting, lower fatty acid serving as a factor for the growth inhibition of plants.
As means for suppressing the above, some processes using various microorganisms have been attempted. In fact, however, any satisfactory effects have not been obtained.
Moreover, the thus obtained compost may be of fine powders like soil, in which decomposed fibers may remain large, so that inconvenience in handling may be arisen for packing, transportation, storage, dispersion, and the like. In particular, such fine powder can be easily scurried when it is dispersed, and thus such compost must be dispersed selectively on unwindy days.
A first object of the present invention is to overcome the above-described conventional problems, and to establish a process for producing compost in a stable manner and in a short period of time by conducting the steps of fermentation and composting for organic waste materials under the aerobic condition, reducing the occurrence period of ammonium and amines causing unpleasant odors, preventing the reoccurrence of such unpleasant odors, and inhibiting. occurrence and accumulation of lower fatty acid (e.g., isobutyric acid, butyric acid, isovaleric acid, and acetic acid) which are inhibitor of the growth of plants.
Also, in order to improve workability for dispersing the compost, the one having a predetermined size and weight will be necessary.
According to the study of the inventors of the present invention, it has been discovered that for the purpose of realizing and sustaining the aerobic fermentation state effective for composting, the oxygen concentration in an organic waste material (hereinafter, sometimes referred to as "material") must be constantly kept at a predetermined value or more, and an appropriate water content in the material must be kept. The present inventors have made intensive investigation and have then discovered that uniform and excellent fermentation with the aerobic bacteria can be achieved by stirring the whole material in a fermentation tank to uniformly sustain the fermentation, supplying oxygen over the entire material, and supplying water to keep the water content of the material at 60 .+-.5%
Further, when the aerobic fermentation is conducted using spent grains as material, during its primary fermentation period, small amount of saccharide (or sugar) contained in the spent grains is initially decomposed, sugars obtained by decomposing hemicellulose or cellulose are then used as an energy source for the growth of microorganisms. On the other hand, the present inventors assume that, when cellulose or the like is slowly decomposed, the aerobic bacteria obtain energy for the growth through the metabolic pathway in which it is decomposed from protein to amines/ammonium through amino acid (hereinafter, referred to as "amine/ammonium metabolic systems"), whereby unpleasant odors may be generated Therefore, it is conceivable that the metabolic system from protein to amino acid is replaced with the metabolic growth system using sugar as an energy source, so that occurrence of such unpleasant odors at the fermentation may be prevented.
This assumption is supported by existence of the report that when sugars such as molasses are added at a time at the beginning of fermentation to compost organic waste materials, such unpleasant odors can be more prevented from occurring in comparison with the case where no sugar is added. According to the study of the inventors of the present invention, however, the fermentation is allowed to slowly proceed under this method of adding at a time (batch addition method), so that not only sugar metabolism but also the fermentation in the protein-amino acid decomposition metabolic system may be possibly activated, and occurrence of such unpleasant odors say not be sufficiently prevented.
Accordingly, in order to solve the above described problems, a second object of the present invention is to control the fermentation so that the subject of the aerobic fermentation may be always fermented through the sugar decomposition metabolism, and therefore to provide a process for adding sugars in a divisional manner at a predetermined timing so that the aerobic fermentation may not transfer to the fermentation based on the protein-amino acid decomposition metabolism, so that the fermentation based on the metabolic growth system using saccharides as an energy source can be conducted, for greatly inhibiting occurrence of the amines and ammonium causing such unpleasant odors at the fermentation, and for producing compost with high quality.